Non-alcoholic fatty liver disease (NAFLD) has reached epidemic proportions in our country, affecting up to a third of the US population. Up to 16 million Americans are estimated to have a progressive inflammatory subtype called non-alcoholic steatohepatitis (NASH), which produces complications such as cirrhosis and hepatocellular carcinoma and is predicted to become the leading indications for liver transplantation in the next decade. There is a startling paucity of treatments for NASH. The role of the innate immune system in triggering the inflammatory cascade in NASH remains unexplored and unexploited. We hypothesize that hepatic macrophages, the earliest innate immune cells seen in the inflammatory infiltrate in NASH, are the key cells responsible for propagating the immune infiltration, tissue destruction and fibrogenesis characteristic of progressive NASH. Preliminary data from our lab shows that a soluble marker of activated macrophages, sCD163, is elevated in progressive NASH and correlates strongly with fibrosis. We have also found that cell-bound CD163 levels are inversely related to sCD163 levels, decreasing in hepatic tissue macrophages as inflammation progresses. We hypothesize that changes in the hepatic CD163+ macrophage population are associated with progressive NASH, resulting in fibrosis and cirrhosis. In Aim 1, we will expand on our current findings with larger sample sizes and quantify the changes in cell-bound CD163 as NASH progresses to confirm whether sCD163 is an ideal biomarker for progressive disease. We will next determine whether elevated serum sCD163 are the cause or effect of progressive inflammation by testing the effects of recombinant sCD163 on cell cultures of primary hepatocytes, stellate cells and macrophages. In Aim 2, we will test the efficacy of two therapies, cenicriviroc (CVC) and liposomal clodronate, to demonstrate that their interference with macrophage activity in in vivo mouse models of NASH retards the progressive inflammatory reaction in NASH. The long term goal of this work is to enhance our understanding of macrophages in progressive NASH, and determine when and how to manipulate this cell type to prevent the catastrophic sequelae of disease, namely, cirrhosis and HCC. The knowledge we will gain about macrophages in the course of this proposal will hopefully apply not only to NASH, but other chronic, inflammatory, fibrotic liver diseases, in which macrophages play a central role.